1. Field of the Invention
The present invention relates to an apparatus and method for efficiently loading feeder optical fibers from fractionally-utilized distribution fibers.
2. Description of the Prior Art
Optical fibers are rapidly becoming the preferred means for transmission in telecommunications systems. The advantages of using optical fibers are well known and are fully accepted as being desirable. Optical fiber transmission provides exceedingly wide bandwidths which will allow for the future provision of broadband services directly to individual subscribers on a relatively universal basis. Such broadband services may include data transmission; however, there is a broader market for the distribution of video services over the telecommunications network to the vast number of residential subscribers.
While the use of optical fibers as the transmission medium is clearly desirable, systems designers are faced with a problem of how to maintain feeder efficiency while distribution fiber efficiency lags during the emergence of the broadband services. The installation of optical fiber transmission systems is a costly undertaking; therefore, these systems must be used as efficiently as possible to provide a rapid return on the investment for the telecommunications company.
There have been many proposals for providing fiber optic services to residential subscribers in both narrowband and broadband format. Some of these proposals have been described in the Description of the Prior Art set forth in the afore-mentioned co-pending application entitled, "Switched Video Architecture for an Optical Fiber-to-the-Curb Telecommunication System". Various articles have been published describing the advantages of fiber optic systems, and in particular, the advantages of certain types of broadband fiber optic systems.
An article entitled: "A Future Switched Video System"by John R. Gunter, IEEE LCS Magazine, February, 1990, at page 66 and following, describes the desirability of providing video services over the telecommunications network. Another article entitled: "A High-Quality Switched FM Video System" by David E. Robinson and David Grubb, III, IEEE LCS Magazine, also published February, 1990, at page 53 and following describes a proposed system architecture wherein the various video channels are frequency multiplexed onto a carrier; however, the carrier uses wavelength division multiplexing for upstream and downstream transmissions.
Other articles describing the simultaneous transmission of narrowband and broadband signals are as follows: "A Hybrid Lightwave Transmission System for Subcarrier Multiplexed Video and Digital B-ISDN Services in the Local Loop", by Charles N. Lo, Journal of Lightwave Technology, Vol. 7, No. 11, November, 1989, pp. 1839-1848; and "Fiber Optic Analog-Digital Hybrid Signal Transmission Employing Frequency Modulation", by K. Sato et al, IEEE Transactions on Communications, Vol. COM-33, No. 5, May 1985, pp. 433-441.
In anticipation of future acceptance by residential subscribers of the full capability of a fiber optic transmission system and, in particular, the use of broadband services, it is desirable to install distribution fibers throughout residential neighborhoods to prepare to handle the future broadband traffic. Unfortunately, these distribution fibers are under-utilized when they initially carry only narrowband traffic, such as Plain Old Telephone Service (POTS).
For design reasons and system simplicity, signals on the distribution fibers within the residential neighborhood normally run at some fixed rate with a standard maximum payload, such as a DS1 payload of 24 DS0 channels. In most neighborhoods, it is difficult to initially utilize the full capability of the payload on distribution fibers; however, this inefficient under-utilization is the price that the telephone service provider must pay for being prepared for future growth.
However, business considerations demand that the more centralized feeder plant and feeder fibers be more efficiently used, so as to minimize the commercial effect of the inefficient distribution plant. Thus, every effort must be made to increase the efficiency of the centralized feeder plant during the emergence of the broadband services.